Expired Carseats

[ebhappydc]

I purchased four good quality carseats from Sears in 2011 and have used them for short trips over the years. I believe they are coming up to expiry date, or have gone past. Am I required to throw them in the landfill now and buy again ?($800+). Seems like such a waste as they still look new and were never in accident. Is it illegal to keep using? Ugh. Does the plastic lose integrity? Thanks. Not sure if my post will show up twice - I tried to submit earlier and it disappeared....